Controlled power circuit with adjusted voltage feedback to regulate the output power

ABSTRACT

A controller to regulate an output voltage of a power converter comprising a feedback reference circuit to generate a drive signal to control a power switch in response to the feedback signal and an output power control circuit configured to generate an adjust signal in response to an output current of the power converter and a desired value of an output power of the power converter, the adjust signal adjusts the feedback signal such that the controller regulates the output voltage to achieve the desired value of the output power. The output power control circuit further comprises an analog-to-digital converter (ADC), a calculator circuit, and an update circuit. The ADC provides a measure signal which is a digital representation of the output current, the calculator circuit determines a calculated value of the output voltage, and the update circuit further outputs an update signal to update the adjust signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/010,071, filed on Jun. 15, 2018, now pending, which is a continuationof U.S. application Ser. No. 15/438,026, filed Feb. 21, 2017, now U.S.Pat. No. 10,027,236, which issued on Jul. 17, 2018. U.S. applicationSer. No. 15/438,026 and U.S. application Ser. No. 16/010,071 are herebyincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Disclosure

The present invention relates generally to power converters and morespecifically power converters with controlled power.

2. Background

Electronic devices use power to operate. Switched mode power convertersare commonly used due to their high efficiency, small size, and lowweight to power may of today's electronics. Conventional wall socketsprovide a high voltage alternating current. In a switching powerconverter, the high voltage alternating current (ac) input is convertedto provide a well-regulated direct current (dc) output through an energytransfer element. The switched mode power converter usually providesoutput regulation by sensing one or more inputs representative of one ormore output quantities and controlling the output in a closed loop. Inoperation, a power switch is utilized to provide the desired output byvarying the duty cycle (typically the ratio of the on time of the switchto the total switching period), varying the switching frequency, orvarying the number of pulses per unit time of the switch in a switchedmode power converter.

The power converter may provide a regulated output current, outputvoltage, or output power. In general, when regulating the output currentto a desired value, the output current is measured and one or moreparameters of the power switch is varied until the output currentreaches the desired value. Similarly, output voltage is generally sensedwhen regulating the output voltage to a desired value. Output power isthe product of the output voltage and the output current. In regulatingoutput power, the output voltage is generally measured and one or moreparameters of the power switch is varied until the output currentreaches the target value which provides the desired output power.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 illustrates one example of a power converter which includes anoutput power control circuit in accordance with teachings of the presentinvention.

FIG. 2 illustrates an example graph of the relationship between outputcurrent and output voltage of the power converter of FIG. 1 inaccordance with the teachings of the present invention.

FIG. 3 illustrates an example output power control circuit shown in FIG.1 in accordance with the teachings of the present invention.

FIG. 4 illustrates another example power converter which includes aprimary controller and a secondary controller coupled to a output powercontrol circuit in a monolithic circuit in accordance with the teachingsof the present invention.

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings. Skilled artisans willappreciate that elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale. For example,the dimensions of some of the elements in the figures may be exaggeratedrelative to other elements to help to improve understanding of variousembodiments of the present invention. Also, common but well-understoodelements that are useful or necessary in a commercially feasibleembodiment are often not depicted in order to facilitate a lessobstructed view of these various embodiments of the present invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one having ordinary skill in the art thatthe specific detail need not be employed to practice the presentinvention. In other instances, well-known materials or methods have notbeen described in detail in order to avoid obscuring the presentinvention.

Reference throughout this specification to “one embodiment”, “anembodiment”, “one example” or “an example” means that a particularfeature, structure or characteristic described in connection with theembodiment or example is included in at least one embodiment of thepresent invention. Thus, appearances of the phrases “in one embodiment”,“in an embodiment”, “one example” or “an example” in various placesthroughout this specification are not necessarily all referring to thesame embodiment or example. Furthermore, the particular features,structures or characteristics may be combined in any suitablecombinations and/or subcombinations in one or more embodiments orexamples. Particular features, structures or characteristics may beincluded in an integrated circuit, an electronic circuit, acombinational logic circuit, or other suitable components that providethe described functionality. In addition, it is appreciated that thefigures provided herewith are for explanation purposes to personsordinarily skilled in the art and that the drawings are not necessarilydrawn to scale.

Output power is the product of the output voltage and the outputcurrent. In regulating output power, the output voltage is generallymeasured and one or more parameters of the power switch are varied untilthe output current reaches the target value which provides the desiredoutput power. However, output voltage changes quickly over time ascompared to the output current and this may result in a constantadjustment of the output current and instability of the control loop.

In embodiments of the present invention, the output current is measuredand the one or more parameters of the power switch are varied until theoutput voltage reaches the target value and the power converter providesthe desired output power. Further, the measurement of the output currentand subsequent calculation of the output voltage to provide a controlledoutput power is implemented digitally.

The controller of the power converter receives a current sense signal,representative of the output current of the power converter and convertsthe current sense signal to a digital current sense signal. The digitalcurrent sense signal is then filtered and stabilized. Using the filteredsignal, the controller calculates the desired output voltage signal andprovides an adjust signal. The adjust signal modifies either a feedbacksignal or a reference signal such that the sensed output voltage reachesa target value which provides the desired output power.

To illustrate, FIG. 1 illustrates one example of a power converter 100including a controller 120 with an output power control circuit 126 inaccordance with the teachings of the present invention. The powerconverter 100 is coupled in a flyback topology with a synchronousrectifier, also referred to as a secondary switch, as the outputrectifier 112. However, it should be appreciated that other convertertopologies could be used as well as non-synchronous output rectifiers,such as a diode. The power converter 100 provides output power to theload 116 from an unregulated input voltage V_(IN) 102. In one example,the input voltage V_(IN) 102 is a rectified ac input voltage. The inputvoltage V_(IN) 102 is received by the energy transfer element T1 104which is shown as including two windings, a primary winding 105 and asecondary winding 106 and is utilized to transfer energy between theinput and the output of the power converter 100. The primary winding 105is coupled to power switch S1 110 which is then further coupled to inputreturn 109. The clamp circuit 108 is shown as coupled across the primarywinding 105 and limits the voltage across the power switch S1 110. Thesecondary winding 106 is shown as coupled to the output rectifier 112,exemplified as a transistor used as a synchronous rectifier. Both theoutput capacitor C1 114 and the load 116 are shown as coupled to theoutput rectifier 112. An output is provided to the load as regulatedoutput voltage V_(O) 117, regulated output current I_(O) 118, or acombination of the two (such as a regulated output power).

The controller 120 is shown as including the output power controlcircuit 126, resistors 128, 130, a comparator 132, and a drive circuit134. The controller 120 is coupled to receive a voltage sense signal 124representative of the output voltage V_(O) 117 and a current sensesignal 122 representative of the output current I_(O) 118. Thecontroller 120 also outputs the secondary drive signal U_(SR) 141, whichcontrols the output rectifier 112, and the primary drive signal U_(PR)142, which controls the switching of the power switch S1 110. Thecontroller 120 controls the output rectifier 112 and the power switch S1110 to regulate the output voltage V_(O) 117, output current I_(O) 118,or output power to a desired value. In one example, the controller 120senses the output current I_(O) 118 to modify the output voltage V_(O)117 to regulate the output power to a desired value.

As shown, the comparator 132 is coupled to receive the reference V_(REF)139 and the feedback signal U_(FB) 138. In one example, comparator 132may be referred to as a reference feedback circuit. In the exampleshown, the voltage sense signal 124 is received by the resistors 128,130, which are coupled as a voltage divider. In one example, theresistors 128, 130 may be referred to as a sense circuit. The feedbacksignal U_(FB) 138 is the output of the voltage divider of resistors 128,130 and as such, the feedback U_(FB) 138 is also representative of theoutput voltage V_(O) 117. In other words, the feedback signal U_(FB) 138is the voltage across resistor 130. The output power control circuit 126receives the current sense signal 122 and the power signal U_(POWER)166. Power signal U_(POWER) 166 is representative of the desired valueof the output power of the power converter 100. In one example, thepower signal U_(POWER) 166 may be set by a user and provided to thecontroller via an interface, such as an inter-integrated circuit (I2C).The output power control circuit 126 outputs the adjust signal U_(ADJ)136 to comparator 132. The output of the output power control circuit126 is coupled between resistors 128, 130 and adjusts the feedbacksignal U_(FB) 138 in response to the output current I_(O) 122.

The output of comparator 132 is the drive signal U_(DR) 140, which isreceived by the drive circuit 134. Drive signal U_(DR) 140 isrepresentative of the switching of power switch S1 110. In other words,the drive signal U_(DR) 140 indicates to the drive circuit 134 whetheror not the power switch S1 110 should be turned on. For the exampleillustrated, the drive circuit 134 receives the drive signal U_(DR) 140and generates the primary drive signal U_(PR) 142 and the secondarydrive signal U_(SR) 141 in response to the drive signal U_(DR) 140. Asmentioned above, the primary drive signal U_(PR) 142 controls openingand closing of the power switch S1 110. It is generally understood thata switch that is closed may conduct current and is considered on, whilea switch that is open cannot conduct current and is considered off. Inone example, the switch S1 110 may be a transistor such as ametal-oxide-semiconductor field-effect transistor (MOSFET). In anotherexample, controller 120 may be implemented as a monolithic integratedcircuit or may be implemented with discrete electrical components or acombination of discrete and integrated components. Controller 120 andswitch S1 110 could form part of an integrated circuit that ismanufactured as either a hybrid or monolithic integrated circuit.

In operation, the power converter 100 provides a regulated outputvoltage V_(O) 117, output current I_(O) 118, or output power P_(O) bycontrolling the transfer of energy between the primary winding 105 andthe secondary winging 106. The transfer of energy is controlled bycontrolling the operation of the power switch S1 110 and the outputrectifier 112. For providing a controlled output power P_(O), thecontroller 120 senses the output current I_(O) 118 to modify the outputvoltage V_(O) 117 to regulate the output power P_(O) to the desiredvalue. The output power control circuit 126 receives the sensed outputcurrent I_(O) 118 and the power signal U_(POWER) 166 and calculates thewanted output voltage V_(O) 117 which would provide the desired outputpower P_(O). The output power control circuit 126 then outputs theadjust signal U_(ADJ) 136, which alters the feedback signal U_(FB) 138.As such, the drive signal U_(DR) 140 is then altered and the outputvoltage V_(O) 117 is modified to a value which provides the desiredoutput power P_(O).

FIG. 2 illustrates a graph 200 of the relationship between outputcurrent I_(O) 218 and output voltage V_(O) 217. The graph 200 furthershows the different operating regions of the power converter 100discussed above with respect to FIG. 1. As shown, the power converterhas three regions of operation: a controlled voltage region 243, acontrolled current region 244, and a controlled power region 245. Forthe controlled voltage region 243, the output voltage V_(O) 217 issubstantially constant while the output current I_(O) 218 may vary, asillustrated by the line parallel with the horizontal axis. In general,the output voltage V_(O) 217 is sensed to regulate the output voltageV_(O) 217 in the controlled voltage region 243. Similarly, for thecontrolled current region 244, the output current I_(O) 218 issubstantially constant while the output voltage V_(O) 217 may vary, asillustrated by the line parallel with the vertical axis. The outputcurrent I_(O) 218 is generally sensed to regulate the output currentI_(O) 218 in the controlled current region 244.

For the controlled power region 245, the line is arched to indicate thatthe output power P_(O) is controlled to a desired value. In one example,the desired value is substantially constant. Examples of the presentdisclosure sense the output current I_(O) 218 to control the outputvoltage V_(O) 217 to a value which regulates the output power P_(O) tothe desired value.

FIG. 3 illustrates an example output power control circuit 326, which isone example of the output power control circuit 126 discussed withrespect to FIG. 1. As shown, the output power control circuit 326includes an analog-to-digital converter (ADC), stabilizing transferfunction circuit 348, controlled power circuit 350, a range decoder 352,and current sources 354, 356 with currents I₁ and I₂, respectively.Further shown in FIG. 3 are resistors 328, 330, which are the same asresistors 128, 130 in FIG. 1. It should be appreciated similarly namedand numbered elements couple and function as described above.

The output power control circuit 326 is coupled to receive the currentsense signal 322 (representative of the output current I_(O)) at the ADC346. The ADC 346 converts the analog sensed output current I_(O) to adigital signal. The output of the ADC 346 is the current measure signalI_(MEASURE) 362, which is an M-bit digital signal representative of theoutput current I_(O). In one example, the current measure signalI_(MEASURE) 362 is an eight-bit digital word. In general, the greaternumber of bits correspond with greater resolution of the measurement ofthe output current I_(O).

The stabilizing transfer function circuit 348 is coupled to receive thecurrent measure signal I_(MEASURE) 362 and outputs the filter signalI_(FILTER) 364. In one example, the filter signal I_(FILTER) 364 is alsoan M-bit digital signal. The stabilizing transfer function circuit 348applies a digital transfer function to reshape the current measuresignal I_(MEASURE) 362 to stabilize the control loop of the controller.The stabilizing transfer function circuit 348 allows the controller togradually change the output voltage V_(O) to a value which regulates theoutput power P_(O). The outputted filter signal I_(FILTER) 364 is afunction of the previously outputted filter signal I_(FILTER) 364, thecurrent measure signal I_(MEASURE) 362, and the constant K:I _(FILTER)(n)=I _(FILTER)(n−1)+K(I _(MEASURE)(n)−I _(FILTER)(n−1))K<1  (1)In one example, the constant K allows adjustment of how quickly thecontroller responds to changes in the output current I_(O). Or in otherwords, the constant K may be used to control the dynamic response of thesystem. The constant K is the proportional gain factor inproportional-integral-derivative (PID) controllers. For example Ksubstantially equal to one corresponds to a very fast response while Ksubstantially equal to zero corresponds to no response. In one example,K is substantially equal to 0.5.

Controlled power circuit 350 is coupled to receive the filter signalI_(FILTER) 364 and outputs the update signal U_(UPDATE) 370. Thecontrolled power circuit 350 also receives the power signal U_(POWER)366, which is representative of the desired value of the output powerP_(O) of the power converter. Power signal U_(POWER) 366 may be providedby to the controller 326 by a user through a digital interface such asan inter-integrated circuit (I2C). The controlled power circuit 350calculates the output voltage V_(O) to provide the desired output powerP_(O) and determines how to update the output voltage V_(O).

As shown, the controlled power circuit 350 includes the calculatorcircuit 358 and the update circuit 360. The calculator circuit 358 iscoupled to receive the filter signal I_(FILTER) 364 and the power signalU_(POWER) 366 and calculates the value of the output voltage V_(O) whichprovides the desired output power P_(O). The calculated value isoutputted by the calculator circuit 358 as the calculated output voltagesignal U_(VOC) 368 and can be described by the function:

$\begin{matrix}{U_{VOC} = \frac{U_{POWER}}{I_{FILTER}}} & (2)\end{matrix}$In one example, the calculated output voltage signal U_(VOC) 368 is anN-bit digital signal. In one example, N is substantially twelve. Thenumber of bits selected for the calculated output voltage signal U_(VOC)368 determines the resolution for how quickly the output voltage V_(O)may be changed.

The update circuit 360 is coupled to receive the calculated outputvoltage signal U_(VOC) 368 and output the update signal U_(UPDATE) 370.As shown, the update signal U_(UPDATE) 370 is received by the rangedecoder 352 and as an input to the update circuit 360. The update signalU_(UPDATE) 370 is representative of how quickly and/or the amount whichthe output voltage V_(O) of the power converter is modified and is alsoan N-bit digital signal. In one example, if the previous value of theupdate signal U_(UPDATE) 370 is less than to the calculated outputvoltage signal U_(VOC) 368 currently received, this may indicate thatthe output power P_(O) is too low and the output voltage V_(O) should beincreased. As such, the update signal U_(UPDATE) 370 is set tosubstantially the calculated output voltage signal U_(VOC) 368 such thatthe controller may vary the output voltage V_(O) to reach the desiredoutput power P_(O). If the previous value of the update signalU_(UPDATE) 370 is substantially equal to the calculated output voltagesignal U_(VOC) 368 currently received, the update signal U_(UPDATE) 370is set to the calculated output voltage signal U_(VOC) 368.

If the previous value of the update signal U_(UPDATE) 370 is greaterthan the calculated output voltage signal U_(VOC) 368 currentlyreceived, this may indicate that the output power P_(O) is too high andthe output voltage V_(O) should be decreased. However, the update signalU_(UPDATE) 370 is not immediately set to the calculated output voltagesignal U_(VOC) 368. This may be done for increased stability. As such,the update signal U_(UPDATE) 370 is set to substantially the previousvalue of the update signal U_(UPDATE) 370 minus a constant P.Mathematically this may be represented:if U _(UPDATE)(n−1)≤U _(VOC)(n) then U _(UPDATE)(n)=U _(VOC)(n)if U _(UPDATE)(n−1)>U _(VOC)(n) then U _(UPDATE)(n)=U_(UPDATE)(n−1)−P  (3)Where the constant P may be a trim option set by a user to determine howquickly the update signal U_(UPDATE) 370 is decreased to substantiallythe calculated output voltage signal U_(VOC) 368. For example, theconstant P could be set to one or two.

The range decoder 352 receives the update signal U_(UPDATE) 370 andoutputs first signal 372 and second signal 374 to the controlled currentsources 354 and 356, respectively. The controlled current sources 354and 356 are coupled together such that the terminal between the currentsources 354, 356 is the output of the output power control circuit 326and provides the adjust signal U_(ADJ) 336. The range decoder 352interprets update signal U_(UPDATE) 370 and determines how much current(via adjust signal U_(ADJ) 336) is sourced or sinked from the resistordivider of resistors 328, 330 via the adjust signal U_(ADJ) 336. Onceinterpreted, the range decoder 352 converts the digital update signalU_(UPDATE) 370 to an analog signal (first signal 372 and/or secondsignal 374) which controls either the current source 354 or currentsource 356. The amount of current I₁ and current I₂ provided by currentsources 354, 356, respectively is controlled by the first and secondsignal 372, 374, respectively. As such, the output power control circuit326 provides the adjust signal U_(ADJ) 336 to adjust the feedback signalU_(FB) 338 to control the output voltage V_(O) to the calculated outputvoltage U_(VOC) 368 determined by the calculator circuit 358.

FIG. 4 illustrates another power converter 400 which includes acontroller 420 which utilizes the output power control circuit 426. Itshould be understood that similarly named and numbered elements coupleand function as discussed above. The power converter 400 is similar tothe power converter 100 illustrated in FIG. 1, however the controller420 includes a secondary controller 476 and a primary controller 478.Primary controller 478 controls the switching of the power switch S1 410via the primary drive signal U_(PR) 442, while the secondary controller480 controls the switching of the secondary switch 412 via the secondarydrive signal U_(SR) 441. As mentioned above, the secondary switch 412may be exemplified as a synchronous rectifier. The primary controller478 and secondary controller 476 may communicate via communication link480. In the example shown, the secondary controller 476 includes theoutput power control circuit 426. In addition, elements of the drivecircuit 134 discussed with respect to FIG. 1 would be included in boththe secondary controller 476 and the primary controller 478. Forexample, the drive signal 140 (of FIG. 1) could be generated by thesecondary controller 476 and communicated to the primary controller 478via the communication link 480.

In one example, primary controller 478 and secondary controller 476 maybe formed as part of an integrated circuit that is manufactured aseither a hybrid or monolithic integrated circuit, which is shown ascontroller 420. In one example the power switch S1 410 may also beintegrated in a single integrated circuit package with controller 420.In another example the secondary switch 412 may be integrated in asingle integrated circuit package with controller 420. However, inanother example, it should be appreciated that both the primarycontroller and the secondary controller need not be included in a singlecontroller package, and for example may be implemented in separatecontroller packages. In addition, in one example, primary controller 478and secondary controller 476 may be formed as separate integratedcircuits.

The above description of illustrated examples of the present invention,including what is described in the Abstract, are not intended to beexhaustive or to be limitation to the precise forms disclosed. Whilespecific embodiments of, and examples for, the invention are describedherein for illustrative purposes, various equivalent modifications arepossible without departing from the broader spirit and scope of thepresent invention. Indeed, it is appreciated that the specific examplevoltages, currents, frequencies, power range values, times, etc., areprovided for explanation purposes and that other values may also beemployed in other embodiments and examples in accordance with theteachings of the present invention.

The invention claimed is:
 1. A controller to regulate an output voltageof a power converter, comprising: a feedback reference circuitconfigured to receive a feedback signal representative of an outputvoltage of the power converter, the feedback reference circuit furtherconfigured to generate a drive signal to control a power switch of thepower converter in response to the feedback signal; and an output powercontrol circuit coupled to the feedback reference circuit, wherein theoutput power control circuit is configured to generate an adjust signalin response to a current sense signal representative of an outputcurrent of the power converter and a power signal representative of adesired value of an output power of the power converter, the adjustsignal adjusts the feedback signal such that the controller regulatesthe output voltage to achieve the desired value of the output power, andthe output power control circuit further comprises: an analog-to-digitalconverter (ADC) configured to receive the current sense signal andprovide a measure signal which is a digital representation of the outputcurrent; a calculator circuit configured to receive a filtered versionof the measure signal and determine a calculated value of the outputvoltage in response to the filtered version of the measure signal andthe desired value of the output power; and an update circuit coupled tothe calculator circuit and configured to receive the calculated value,the update circuit further configured to output an update signal toupdate the adjust signal, wherein a current value of the update signalis substantially equal to the calculated value if a previous value ofthe update signal is less than the calculated value.
 2. The controllerof claim 1, wherein the feedback reference circuit comprises acomparator configured to compare a reference signal to the feedbacksignal.
 3. The controller of claim 1, wherein the output power controlcircuit further comprises a stabilizing transfer circuit coupled to theADC and configured to receive the measure signal and to output thefiltered version of the measure signal to the calculator circuit, thestabilizing transfer circuit further configured to apply a digitaltransfer function to reshape the measure signal.
 4. The controller ofclaim 1, wherein the update circuit is configured to output the updatesignal to update the adjust signal, wherein the current value of theupdate signal is substantially equal to the calculated value if theprevious value of the update signal is less than or equal to thecalculated value.
 5. The controller of claim 1, wherein the currentvalue of the update signal is substantially equal to the previous valueof the update signal minus a constant if the previous value of theupdate signal is greater than the calculated value.
 6. The controller ofclaim 5, wherein the output power control circuit further comprises: arange decoder configured to receive the update signal and output a firstand second signal; and a first and second current source coupled to therange decoder and configured to receive the first and second signal, thefirst and second current source further configured to generate theadjust signal.
 7. The controller of claim 6, wherein the adjust signalis the difference of the first current source and the second currentsource.
 8. The controller of claim 1, wherein the power signal isreceived through an interface, wherein the interface comprises aninter-integrated circuit (I2C).
 9. The controller of claim 1, whereinthe controller further comprises a drive circuit coupled to the feedbackreference circuit and configured to generate a secondary drive signal tocontrol switching of an output rectifier of the power converter inresponse to the drive signal.
 10. The controller of claim 1, wherein thecontroller further comprises a drive circuit coupled to the feedbackreference circuit and configured to generate a primary drive signal tocontrol switching of the power switch in response to the drive signal.11. The controller of claim 1, wherein the controller further comprisesa secondary controller coupled to a secondary side of the powerconverter, wherein the secondary controller comprises the feedbackreference circuit and the output power control circuit, the secondarycontroller configured to generate a secondary drive signal to controlswitching of an output rectifier of the power converter in response tothe drive signal; and a primary controller coupled to a primary side ofthe power converter and configured to generate a primary drive signal tocontrol switching of the power switch in response to the drive signal.12. The controller of claim 11, wherein the secondary controller and theprimary controller are included into a single integrated circuitpackage.
 13. The controller of claim 12, wherein the secondarycontroller and the primary controller are configured to communicate viaa communication link.
 14. The controller of claim 12, wherein thesecondary controller, the primary controller, and the power switch areintegrated into a single integrated circuit package.